BT848 ETC, BT848 Datasheet - Page 69

• Manufacturer Part Number: BT848
• Description: Single-Chip Video Capture for PCI
• Manufacturer: ETC

Autodetection of NTSC or
Brooktree
Analog Signal Selection
PAL/SECAM Video
Considerations
®
Multiplexer
Input Interface
The Bt848 contains an on-chip 3:1 mux while the Bt848A/849A includes an
on-chip 4:1 mux. This mux can be used to switch between three composite sources
or two composite sources and one S-video source. In the first configuration, con-
nect the inputs of the mux (MUX0, MUX1 and MUX2) to the three composite
sources. In the second configuration, connect two inputs to the composite sources
and the other input to the luma component of the S-video connector. In both con-
figurations the output of the mux (MUXOUT) should be connected to the input to
the luma A/D (YIN) and the input to the sync detection circuitry (SYNCDET). The
Bt848A/849A does not require MUXOUT be connected to SYNCDET. When im-
plementing S-video, the input to the chroma A/D (CIN) should be connected to the
chroma signal of the S-video connector.
one video source is required, the source may be connected directly to YIN and
SYNCDET.
The multiplexer is not a break-before-make design. Therefore, during the multi-
plexer switching time it is possible for the input video signals to be momentarily
connected together through the equivalent of 200 .
If the Bt848 is configured to decode both NTSC and PAL/SECAM, the Bt848 can
be programmed to automatically detect which format is being input to the chip.
Autodetection will select the proper clock source for the format detected, (if NTSC
is detected, XTAL0 is selected; if PAL/SECAM is detected, XTAL1 is selected.)
ber of lines in a frame. Based on the result, the format of the video is determined,
and XT0 or XT1 is selected for the clock source. Automatic format detection will
select the clock source, but it will not program the required registers.
E
I
NTERFACES
Use of the multiplexer is not a requirement for operation. If digitization of only
The multiplexers cannot be switched on a real-time pixel-by-pixel basis.
The Bt848 determines the video source input to the chip by counting the num-
LECTRICAL
L848A_A
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